Use of non-volatile based portable storage devices (“PSDs”) for transferring data from one location to another has been rapidly increasing over the years because they are portable, and they have small physical size and large storage capacity. Storage devices come in a variety of designs. Some storage devices are regarded as “embedded”, meaning that they cannot, and are not intended to, be removed by a user from a host device with which they operate. Other storage devices are removable, which means that the user can move them from one host device to another, or replace a storage device with another.
Other storage devices, which are commonly known as “Disk-on-Key” devices, are provided with a Universal Serial Bus (“USB”) interface in order to allow them to be connected to a computer system, for example. A flash storage device that is provided with a USB interface is also known in the field as a USB Flash Drive, or “UFD”. MultiMedia Card (“MMC”), Secure Digital (“SD”), miniSD, and microSD, are exemplary flash storage devices that are used with a variety of host devices such as multimedia players (e.g., MP3 and MP4 players), digital cameras, computer laptops, Global Positioning System (“GPS”) devices, and so on.
One use case for PSDs involves the transfer of very large files, such as movies, for home entertainment consumption. “Very large files” are files whose size is, for example, 4 gigabytes (“GB”) or greater. The speed of reading or writing very large files may be insufficient or annoying. For example, while the speed of reading data from a PSD is generally satisfactory for viewing movies, the relatively slow speed of writing such movies onto a PSD drive implies waiting several minutes (e.g. 3-4 minutes) for copying a 4 GB movie onto the PSD (using a typical write speed of 18 megabytes per second (“MB/s”)), which is unsatisfactory for many users. Writing large files into a storage device takes a long time because of the way data is written into a flash memory; i.e., data is written in pages, one page after another, and voltages associated with the data writing are iteratively rechecked against predefined thresholds.
FIG. 1 shows a typical portable storage device (“PSD”) 100. Portable storage device 100 includes a USB connector 110, a storage controller 120, and a storage area 130 that includes two separate flash memory units 140 and 150. Storage controller 120 manages transfer of data to/from storage area 130 while handling flash memory units 140 and 150 as a single, unified, storage area (i.e., storage area 130), where handling flash memory units 140 and 150 as a single, unified, storage area means that storage controller 120 addresses flash memory units 140 and 150 using a single file system. Each of flash memory units 140 and 150 can be a flash memory chip, a flash memory die, or a flash memory package. USB connector 110 has a typical electrical pin layout as illustrated in FIG. 2.
Referring to FIG. 2, it schematically illustrates a 4-pin layout usable by standard USB connectors. Pins 1 and 4 provide electrical energy from a connected host (not shown in FIG. 2) for energizing PSD 100. Pins 2 and 3 transfer electrical signals that correspond to transferred data.
The conventional storage device's architecture of FIG. 1 has been designed with the notion that small data files can be transferred to, or from, a storage device using low bit rates because transferring such files would not take much time because of the files being small. However, the conventional storage device's architecture of FIG. 1 is inefficient (i.e., in terms of data transfer speed) when it comes to large data files. There is thus a need for a PSD with increased data transfer speed. In particular, there is a need for a PSD with increased data writing speed.